1. Field of the Invention
The present invention relates to a sound reproducing loudspeaker and, more particularly, to a damper for supporting the vibratory system including a diaphragm of a sound reproducing loudspeaker.
2. Description of the Prior Art
Referring to FIG. 15 showing a conventional sound reproducing loudspeaker in a sectional view, there are shown a magnetic circuit element 1 of a magnetic material having a central projection 1a at its center, a ring-shaped magnet 2 attached to the upper surface of the periphery of the magnetic circuit element 1, a flat ring-shaped pole piece 3 attached to the upper surface of the magnet 2, a conical speaker frame 4 having a lower end fixed to the upper surface of the pole piece 3 and expanding upward, a bobbin 5 put over the projection 1a so as to surround the projection 1a, a conical diaphragm 6 having a lower edge joined to the circumference of the upper end of the bobbin 5, and an upper edge joined to the upper edge of the speaker frame 4 with an edge member 7, a dust cap 8 attached to the diaphragm 6 so as to cover the upper part of the bobbin 5, a voice coil 9 wound around the lower end of the bobbin 5 opposite to the inner circumference of the pole piece 3, and a damper 10 placed substantially horizontally between and joined to the outer circumference of the bobbin 5 and the inner circumference of the speaker frame 4.
As shown in FIGS. 16 and 17, the damper 10 is a substantially ring-shaped plate having radially alternate circular ridges and circular furrows. The damper 10 is formed by impregnating a piece of woven fabric consisting of meshed fibers R and S extending along an X-axis and a Y-axis respectively as shown in FIG. 16 with a resin, and then forming the resin-impregnated piece of woven fabric in a wave shape.
In operation, an acoustic reproducing signal is supplied to the voice coil 9 of the sound reproducing loudspeaker. Then, the diaphragm 6 vibrates according to the varying intensity of the acoustic signal to convert vibrational energy into sound energy. The diaphragm 6 is held mechanically by the edge member 7 and the damper 10. The amplitude of vibration of the diaphragm 6 is dependent on the intensity of the current flowing through the voice coil 9. The respective displacements of the edge member 7 and the damper 10 are generated proportionally to the vibrational energy of the diaphragm 6.
Generally, when the diaphragm 6 vibrates, the damper 10 is required to meet antinomic conditions that the displacement of the damper 10 supporting the diaphragm 6 is proportional to the amplitude of the diaphragm when the amplitude is comparatively small and that the damper will not damp the vibrations when the amplitude of the vibration of the diaphragm 6 is nearly equal to a limit amplitude. Therefore, if importance is attached to damping ability, the damper 10 will not be displaced correctly according to the variation of the current flowing through the voice coil 9 when the amplitude is comparatively small.
When the meshed component yarns R and S of the damper 10 are extended along the X-axis and the Y-axis respectively, the moduli of elasticity in the direction of bending at portions of the damper around lines extending at an angle of 45.degree. to the X-axis and the Y-axis is higher than that of other portions, and deformation rigidity thereabouts is also higher than that of other portions. FIG. 18 shows the distribution of modulus of elasticity on the damper 10. As is obvious from FIG. 18, the moduli of elasticity on inner circles are greater than those on outer circles, and modulus of elasticity increases gradually with angle from the X-axis and the Y-axis from a normalized value 1 on the X-axis and the Y-axis and reaches a maximum greater than the normalized value 1 at a position on lines at an angle of 45.degree. to the X-axis and the Y-axis. Since the inner periphery 10a of the damper 10 is close to the source of vibrational energy as shown in FIG. 17, it is desirable to form the inner periphery 10a of the damper 10 in a construction having a high strength and a high flexural rigidity.
In the conventional sound reproducing loudspeaker thus constructed, in some cases, the diaphragm 6 is not displaced in proportion to the intensity of the current flowing through the voice coil 9 to vibrate the diaphragm 6 due to irregular strength distribution on the damper 10 and the insufficient strength of the inner periphery 10a of the damper 10. Furthermore, the forward movement and the rearward movement of the diaphragm 6 along the longitudinal axis differ from each other when the diaphragm 6 vibrates in longitudinal directions causing hysteresis and, consequently, vibrational linearity cannot be secured.
In particular, when the damper 10 has an irregular strength distribution and the resolution of the central part of the damper 10 for discerning acoustic signals in a range of minute vibrations from each other is deteriorated, sounds and voices having large amplitude cannot be reproduced in a high fidelity due to the aforementioned hysteresis. Techniques analogous with those connected with this conventional sound reproducing loudspeaker are disclosed in Japanese Patent Laid-open (Kokai) No. 6-62494.